Ethernet is ubiquitous in enterprise networks where it is used to facilitate communication between computers. Each device that communicates via an Ethernet network is assigned a unique Medium Access Control (MAC) address. An Ethernet switch typically determines a destination port for each packet it receives based on learning MAC addresses of packets previously received by the switch.
Due to its many attractive features, Ethernet is now common in service provider networks as well as enterprise networks. Since service provider networks may have thousands of devices connected to them, a service provider packet switch may need to learn a large number of MAC addresses.
The service provider packet switch typically stores these MAC addresses in high-speed memory. In order to store a large number of MAC addresses, a large amount of high-speed memory is required. This large amount of high-speed memory tends to make Ethernet service provider packet switches expensive.